Thor Vikström bought his island in the 1960s for $5,000. His goal was to protect and preserve its 7 acres.

Mr. Vikström could see the island, Île Ronde, across a narrow stretch of river from his home near Montreal. He and his family explored it often – at one point they even built a cable ferry across. But the rules were clear: Leave the environment as untouched as possible.

“[My dad would] get mad at us because we left a Coke bottle on the island,” son Hans Vikström told the Canadian Broadcasting Corp.

Over the years the surrounding area, wedged between fast-growing suburbs and the city, became built-up and expensive. Developers came calling, offering increasingly high bids for Île Ronde. 

Mr. Vikström rebuffed them all, saying nature was more valuable than money in his pocket. In December he donated the island to the Nature Conservancy of Canada so the metropolitan area would have a guaranteed spot of green.

In the spring, flocks of wood ducks and other waterfowl land near the island and raise chicks in its cover, Mr. Vikström said when announcing his gift. Turtles sun themselves on the shore. The forests are full of shagbark hickories, a spectacular tree whose bark appears to be falling off like old clothes.

“It is a dream for me now that it is preserved forever,” Mr. Vikström says.

The Nature Conservancy of Canada says it’s thrilled with the gift of valuable land so near an urban center. Individual donations can combine into major collective environmental protection, Joël Bonin, a development and communications official with the organization’s Quebec chapter, told The Washington Post.

“Every time someone makes a gift, it’s for everyone,” said Mr. Bonin.